Electric system



Aug. 1, 1944.

w. N. TUTTLE 2,354,718

ELECTRONIC SYSTEM Filed Nov. 8, 1941 2 Sheets-Sheet l ELECTRONIC SYSTEMFiled Nov. 8, 1941 2 Sheets-Sheet 2 -from the rectified voltage PatentedAug. -1,' 1944 ELECTRIC SYSTEM William Norris Tuttle, Concord, Mesa,assignor. to General Radio. Company, Cambridge, Mass,

a corporation of Massachusetts Application November 2;, 1941, Serial No.418,336

47 Claims.

The present invention relates to electric systems. From one aspect, theinvention relates more particularly to amplifiers. From another aspect,the invention relates more particularly to vacuum-tube voltmeters.

One type of vacuum-tube meter for the measurement of alternatingvoltages comprises a rectifier for developing a direct-current voltagefrom rent amplifier for developing sumcient power to operate anindicating meter. Degenerative coupling may be employed in the amplifierto stabilize the gain and insure permanence of calibration. The use oftwo-stage degenerative direct-currenmamplifiers in meters of thischaracter, however, has been accompanied by unsatisfactory operation.

It is not easy, for example, to produce a de-' sign such that theopposing currents shall exactly balance, leaving no residual currentthrough the degenerative resistor without, at the same time,

substantially reducing the over-all gain of the system. The difficultieshave usually been overcome by providing the amplifier with a furtherstage or Stages. V

An object of the present invention, however, is to provide a two-stagedegenerative direct-current amplifier or voltmeter, in which theresidual current through the degenerative resistor balanced out whilemaintaining maximum gain of the separate stages.

Since the current through the degenerative resistance is zero when themeter reads zero, this resistance can be varied over wide limits withoutaffecting the zero setting. A further object of the present invention,therefore, is to provide a direct-current amplifier the sensitivity ofwhich can be varied over wide limits without simultaneous compensationof the zero adjustment.

Another object of the invention is to provide a novel amplifier.

proposed, although the operating potential can be provided for thescreen electrode by means of voltage-dividing resistor circuits ordropping rethe applied alternating voltage, and a direct-cur- Stillanother object is to provide a simplified degenerative direct-currentamplifier.

A further object is to provide a novel voltmeter of which the amplifiermay constitute an element.

In prior-art degenerativecircuits, it has been dimcult to provide aconstant voltage bias for the screen grid without the aid of separatebattery supplies.

In the use of a screen-grid tube in direct-current amplification,high-voltage gain can be obtained in a single stage provided that thescreen electrode can be maintained at a'constant potential with respectto the cathode, independent of the applied signal voltage. In circuitspreviously sistors, the currents through these resistors tend to varysubstantially with the applied signal so that a constant screenpotential is not obtained and reduction in voltage gain results. y Inamplifiers for altematingecurrent voltages, these effects can becorrected by by-pass condensers which, of course, can not be applied tothe design of direct-current amplifiers.

ti n, the plate battery of one of the two tubes is utilized as thescreen battery forthe other without any resistor circuits beingrequired, thus permitting the maximum possible voltage 'gain which maybe'obtained from screen-grid amplifiers.

Other and further objects will be explained hereinafter and will beparticularly pointed out in the appended claims.

The invention will now be more fully described -in connection with theaccompanying drawings, in which Fig. 1 is a simplified circuit diagramillustrative of the amplifier feature of the invention; Figs. 2 and 3are similardiagrams, with further complications; and Fig. i is a similardiagram, illustrating -a voltmeter embodying the present invention. c

The illustrated two-stage amplifier comprises two vacuum tubes 2 and 4.The tube 2 is provided with a cathode 6, shown as a filament, en

ergized, by a cathode battery or other voltage source I, an anode 8, anda control electrode 3.. The tube 4 is provided with a cathode l2, shownas a filament, energized by a cathode battery or other voltage source I3, an anode l4 and a control electrode IS.

The vacuum tube 2, with its input and output circuits, constitutes thefirst stage of the twostage amplifier. The external voltage to beamplified may be impressed across input terminals i8 and 28 of the inputcircuit of the tube 2. Referring first to Fig. 1, this input circuitextends from one input terminal l8, by way of a conductor 20, andthrough an impedance 22, shown as a resistor, to a junction-pointterminal 23; thence, by way of a conductor 26, to the cathode 8; thence,through the space in the vacuum tube 2, to the control electrode l0; andfrom the control electrode it], by way of, a conductor 26, to the otherinput terminal 28. For reasons hereinafter stated, the resistor 22 actsas a degenerative resistor. The output circuit of the firstvacuum tube 2of the two-stage amplifier extends from the cathode B,

through the space in the tube 2, to the anode. 8;

- According to .a ieature of the present inventhence, by way of aconductor 38, through an output impedance 32, shown as a resistor, tothe positive pole of a plate or anode or B-battery voltage source 34;from the negative pole of this battery 34, to a Junction-point terminal35; and, by way of a conductor 38, through an indicating instrument 33and the impedance 22 and, by way of the conductor 24, back to thecathode 3.

The vacuum tube 4, with its input and output circuits, constitutes thesecond stage of the twostage amplifier. The input circuit of the tube 4is connected across the output impedance 32 and the battery 34 in theoutput circuit of the tube 2. The output impedance 32 of the first tube.2 thus constitutes the. input impedance of the second tube 4 operatingas the customary platecoupling resistor. This input circuit extends fromthe terminal 35, by way of a conductor 40, to the cathode -l 2; throughthe space in the vacuum tube 4, to the control electrode l5; and fromthe control electrode tery 44, by way of a conductor 42, to the coneductor 33, the anode 3. The input circuit of the tub 4 continues fromthe conductor 42, through the impedance 32 and the battery 34, backto'the terminal 35. The output circuit ofthe second vacuum tube 4 may betraced from the cathode i2, by way of ,the conductors 40 and 35, theindicating instrument 33 and the impedance 22, to thetermlnal 23, whichis connected to the negative pole of a plate or anode or B-batt'eryvoltage source 48; from the positive pole of this battery 48, by way theanode I4; and from the anode l4, through the space in the tube 4, backto the cathode I2.

The B-battery voltage source 341s connected between the anode 8 of thetube 2 and the cathode l2 of the tube 4, with its negative poleconnected to the cathode l2 and its positive pole to the anode 3. Theconnections may be traced from theanode 8, by way of the conductor 30,through the impedance 32 and the battery34, to the terminal 35 and, byway of the conductor 43, to the cathode l2. The B-battery voltage source46 is similarly connected between the anode of the tube 4 and thecathode i of the tube 2, with its negative pole connected to the cathode6 and its positive pole to the anode I4. The connections may be tracedfrom the anode l4, byway of the conductor 43, through the battery 43, tothe terminal 23 and, by way of the conductor 24, to the cathode 3.

The system, as so far described, resembles what is popularly known as'adirect-current amplifier; for, though the voltage across the impedance22 is somewhat less than that applied to the terminals 18 and 23, thepower developed across 2,354,718 which includes the indicatinginstrument 33, is

connected at one end to the junction point 23,

between the negative terminal of the battery 46' and the conductor 24that leads to the cathode 6.

-It is connected at the other end to the Junction point 35, between thenegative terminal of the battery 34 and the conductor 40 that leads tothe cathode. The impedance 22 and the indicating instrument in thiscommon portion of the output circuits, between the cathodes G and I2,that the batteries 34 and 46 send current therethrough in oppoit,through. a biasing batthat. connects the impedance 32 to through of aconductor 43, to

' site directions.

in plate current The operating points of the tubes 2 and 4, or of one ofthem, may be so chosen that the opposing currents in this common portionof the output circuits shall balance with extreme accuracy at times whenit is preferred that the indicating instrument 33 should read zero.

Since the impedance 22, which is connected in the common portion of theoutput circuits of the tubes 2 and 4, is connected also in the inputcircuit of thefirst tube 2, the amplified current from the tube 4through this impedance 22, when an external voltage; is impressed acrossthe terminals l8 and 28, is in -a direction opposite to that of theexternal voltage in the input circuit of the first vacuum tube 2 of theamplis her. It is for this reason that the resistor 22 may be referredto as a degenerative resistor. Although the current through the resistor22 is derived largely from the tube 4 because of the amplificationof thepreceding stage, the change is the result of the action of both tubes,because both tubes operate in such a sense that they both aid in theproduction of the degenerative voltage across the resistor 22. Thecurrents through the indicating instrument 33 from the'two tubes 2 and 4are thus also in the same direction. .To state it otherwise, theincremental changes in the output circuits from both tubes 2 and 4resulting from the external voltage applied to the terminals l3 and 28thus add up to yield a current in the same direction through theimpedance 22 and the indicating instrument 33, though producing avoltage opposite in direction to the voltage applied at the terminals l8and 23 to the input circuit of the the impedance 22 may be very muchgreater than that taken from the voltage source across the terminals l3and 23. The voltage across the impedance 22 may build up to a valuesubstantially equal to the applied input voltage, if sufllcient tube 2.

' Three features. among others, may be emphasized: first, thedegenerative properties of the impedance 22; secondly, the function ofproducing balance in the currents through the common portion of theoutput circuits; and thirdly. the property whereby the incrementaloutput currents from the tubes 2 and 4 cumulate to produce a currentthrough this impedance 22 in the same direction.

The resistance of the impedance 22 may be considerably less than theresistive impedance of the indicating instrument 33, which latter may bequite high, without adversely affecting the operation of the system.This has a bearing upon the sensitivity of the system. By making theimpedance 22 variable, it may be caused to provide a sensitivitycontrol, .as more fully described hereinafter.

Another advantage is that, since the terminal l3 may be at the lowvoltage of the ground, and as the indicating instrument 33 is subjectedto this low voltage, it is possible to use instruments 33, likerecording meters, that could not be used in circuits where they would besubjected to high voltages.

The gain of the amplifier without degenera- 33 are thus so connected tleenergy gain is available to'provide the overall degeneration that isdesired to be used for stabilizing the over-all gain.

According to the present invention, on the other hand, there is nodegenerative operation to reduce the gain of the two individual stagesof this two-stage amplifier. No degeneration takes place to,reduce thegain 01' the second tube, for

example, because the voltage across the impedance 32 is the onlyvariable voltage in its input circuit: I The degeneration, therefore,can be applied with maximum eifectiveness. It follows that each of thetubes 2 and 4 contributes its maximum gain to the over-all amplificationgain of the system. This, moreover, is accomplished with a minimumnumber of independent voltage sources, namely, two plate batteries 34and 43 and one bias battery 44.

The invention thus provides a simple portable direct-current amplifieremploying two tubes 2 and- 4, with only four batteries from whichcurrent is drawn, two of which are the anodeor B batteries. 34 and 46,and the other two of which are the cathode batteries 1 and I3. Nocurrent, or course, is drawn from the bias battery 44. With battery-typetubes 2 and 4, single-cell filament-bathode batteries 1, and I3 may beemployed. 1

If the resistance of the degenerative resistor "22, moreover, is largecompared with the reciprocal of the trans-conductance of the two-stageamplifier, that is, the ratio of the input voltage to the first tube2to'the output current through the common impedance 22, then the gain issubstantially independent of changes in gain in the amplifier. I 1

As is generally true with degenerative directcurrent amplifiers of thischaracter, variations inv the zero reading of the meter 33 due tochanges in the plate-battery voltages and in the filament battery ofthesecond tube 4 are largely neutralized.

The circuit of Fig. l is reproduced in Fig. 2, but with the tube 2 shownas a pentode, instead of a triode; in addition to the cathode 6, thecontrol electrode Hi and the anode 3, it comprises a screen electrodeand a further electrode 52.

In Fig. 2, also, the bias battery M is omitted and the requiredoperating potential for the grid 66 of tube 5 obtained by returning thecathode I2 The further electrode 52 is connected in usual fashion, by aconductor 53, to the cathode 6, and

the further electrode 53, bya conductor 60, to

the cathode l2. The screen electrode 54 of the tube 4 is subjected tothe voltage of the battery 34 of the tube 2 by means of a conductor 62that joins the screen electrode 54 to a junction-point terminal 64between the impedance 32 and the positive pole of the battery 34. Thescreen electrode 50 of th tube 2 is similarly subjected to the voltageof the battery 46 of the tube 4 by a conductor 66. The conductor 66,however, 'connects the screen electrode 50 to'a. variable tap 01' apotentiometer resistor 68 that is connected in shunt to the battery 43.The conductor 52, of

, course, may similarly connect variably the screen electrode 54 to. asimilar variable resistor (not shown) connected across the battery 34.This may be in addition to, or in substitution for, the variableconnection of the screen electrode 50 to the resistor 68 by theconductor 66. g

A voltage bias for the screen electrodes 50 and 54 is thusprovided-without the aid of additional batteries, the plate battery 34of the tube 4 serving as the screen battery of the tube 2, and the platebattery 46 of the tube 2 serving as the screen battery for'the tube 4.

By adjusting the tap of the screen electrode 50; v as by means of theconductor 86 upon the resistor 68, a zero control adjustment may beprovided, independent of the setting of the sensitivity-controlimpedance '22, for adjusting the voltage from the potentiometer 65applied to'the screen electrode 50.

In .many prior art circuits, the advantages of 'the screen-gridoperation claimed therefor are more apparent than real. This is becausevariations in the plate current of either of the tubes connected. Whenthe indicating instrument 33 is included in the circuit, however, asensitive direct-current vacuum-tube voltmeter is provided to anintermediate point 69 on the battery 34,

This arrangement therefore employsonly two teries.

In Figs. 3 and 4, the tube 6 is also shown as a pentcde, the screenelectrode being shown at 54 and the further electrode at 56. In theseFigs. 3 and 4, furthermore, an additional impedance 63, shown as aresistor, is illustrated as connected in the conductor 24, between theterminal 23 and 'the cathode 8, in the input circuit of the tube 2. Thismay serve to provide additional bias for the cathode 6. This resistor 59is omitted from Figs. 1 and 2, because the tube 2 can be operated at thepotential of the negative and of the cathode 8;

by the present invention, as the input voltage can be measured intermsof .the output current in the impedance 22 with its aid.

In order to reduce the grid or input current in'the tube 2 to a very lowvalue, it is sometimes desired to operate at relatively very low plateand screen voltages. Under these operating conditions, the currentthrough the tube 2 may not be suflicient to balance in the indicatinginstrument 33 the current from the other tube 4, so as to reduce thereading of the indicating instrument 33 to zero. This difliculty may beovercome, and the first tube 2 may be operated at any de-- sired part ofits characteristic, by taking additional current through an auxiliaryresistor 10, connected between the positive terminal 64 of the battery38 and the cathode 6 of the tube 2 as illustrated in Fig. 4. The currentthrough this resistor 10 thus supplements the current through the firsttube 2 inbalancing the indicating instrument 33 to zero.-

The two-stage directcurrent amplifier above described may be combinedwith'a desirable type of rectifier, shown in Fig. 4 as a diode rectifierI2, to produce an extremely sensit ve alternatin energizing its cathodefilament l5. Asshown, the

= put terminals ll 'of the, rectifier 12, across a Various taps of theresistors output of the rectifier 12 is and 22, and its input to anydesired source of alternatingvoltage by means of input terminals 14 andIt. The diode 12 constitutes, with a condenser 11, a half wave dioderectlflercircuit forrectifying alternating voltage impressed at theterminals I4 and IS. The alternating-current components of the rectifiedvoltage are removed by the filtering network consisting of the resistor80 and the condenser 84.

It is sometimes desirable toemploy a resistance input multiplier betweenthe diode rectifier 12 and the direct-current vacuum-tube voltmeter. Avariable shunt impedance 18, shown as a resistor, perating inconjunction with the filtering series resistor 80, connected in theoutput circuit resistor 88, constitutes apotentiometer for subdividingthe direct-current voltage developed by the'diode rectifier 12. Due tothe initial space current of the diode l2, variations in the zerovoltage will sometimes be produced when varied. These may viding foreach setting be compensated for by proof the resistor I8 an adjustablepotentiometer across the filament-battery" of the diode 12, so that thezero may be pre-set for each voltage range provided by the potentiometerI8, 80

connected to the inthe shunt resistance 18 is correspondingconnected-together contact mem- I required, multi- This adjustablepotentiometer may comprise 86 disposed, in parallel series with aresistor 9|. 88 may be connected, by conductors 82, to three contactmembers 90. Four additional contact members 90 are conaplurality ofresistors with the battery I3, in

nected together to the negative end of the fllamentary cathode 13 ofthe-diode 12. The contact members 90 may be controlled by a deck 84 of athree-deck master switch 92, shown more particularly in Fig. 4. The deck94 is connectedby a conductor 93 to the conductor 20. Correspondingcontact members 85 are connected to the resistor 18 by a second deck 98..The third deck 96 similarly cooperates with contact members 9|.

The "three-deck switch 02 may assume seven positions in clockwisesequence, corresponding to 0.3, 1, 3, 10, 30, 100 and 300 voltsfull-scale, as indicated on the dial I00, in Fig. 4. All seven rangescan be obtained by setting thethree-deck switch 92. In each position, iteffects an adjustvment of each of the resistors 22 and" and acorresponding adjustment to restore the zero of the multiplier, as willnow be explained;

For the first tour voltage ranges correspond ing. as shown, to 0.3, 1, 3and 10 voltage fullscale. the sensitivity may be varied by means of thedegenerative resistor 22. The deck 94, as before stated, controls thezero correction; but since, when changing from one to another of thesefour ranges, no correction gf the zero is required, the correspondingfour -contact members 05 are shown connected together in the mannerbefore described. For the three higher ranges of the instrument,corresponding to 30, 100 and 300 volts full-scale, however, thepotentiometer 10. I is employed to increase the range. It is value forthe three highest ranges 30, 100 and 300,

the three corresponding contact members 9! of which are, therefore,shown The third deck 98, for controlling the value of the resistor 18 ofthe potentiometer I8, 80, leaves this resistor 18 at maximum value forthe first four ranges 0.3, 1, 3 and 10, as indicated by the the highestranges, 30,

bers 95, but operates to give plying action for the three 100 and 300.

A small portable instrument built in accordance with the above designand employing an indicating-meter instrument 33 of 100 microamperesfull-scale sensitivity has been made to' yield a fullescale reading on300 millivolts al- .ternating current covering a frequency range of from20 cycles to a hundred megacycles.

The following values of the various elements have been found to yield avery satisfactory'instrument:

Battery 44 Vo1ts 7.5 Resistor 32 megohms 10 Resistor 68 1 do- 2 Resistor49 ohms 15,000 Resistor i0 megohm 1 I i-position resistor 18 -do 0.35, 1and Resistor 80 do Resistor 88 2do 50 Resistor 8| ohms 800 Resistors 80rnegohm each; 0.1 Condenser 84 microiarad .02 Condenser I'I do .06

- mately this voltage.

resistance of the resistor 22 should be "about The resistor 22 will havea value depending on the required direct-current sensitivity of theportion of the instrument following the rectifier On the range giving l0volts alternating current full scale, for example, the rectifiedvoltage-will be approximately 14 volts for full scale. The metervcurrent of micro-amperes flowing through the resistor Hence, for thisrange, the

140,000 ohms. The approximate value of the resistor 22' may be similarlydetermined for the other ranges. In any particular case, it may beadjusted to the exact desired value, during the final calibration of theinstrument.

'The tubes 2 and 4 may be of the type and the tube 12 of the 95'1type.If the tubes 2 and l are pentodes, asillustrated in Fig. 3, theB-batteries 34 and 46 may, for example, be of 30 volts each. I

Modifications will occur to persons skilled in the art and all suchmodifications are considered to fallwithin the spirit and scope of theinvention, as defined in the appended claims.

What .is claimed is:

1. An electric system having,-in combination. two vacuum tubes each.provided with a cathode, an anode, a control electrode and a screenelectrode, input circuits in which the cathodes and the controlelectrodes of the respective tubes are respectively connected, outputcircuits in which the cathodes and the anodes of the respective tubesare respectively connected, the output circuits each being provided withasource of voltage, means for subjecting the screen electrode of eachtube to the voltage of the voltage source of the output circuit of theother tube, a resistor, andmeans for connecting the anode of one tube tothe screen electrode of the other tube through the resistor.

2. An electric system having, in combination,

two vacuum tubes each provided with a cathode, w

an anode, a control electrode, a screen electrode,

connected together.

:2 must develop approxltube.

and a further electrode, input circuits in which the cathodes and thecontrol electrodes of the respective tubes are respectively connected,output circuits in which the cathodes and the anodes of the respectivetubes are'respectively 5 connected, means connecting the furtherelectrode oi. each tube to the cathode of the same tube, the voutputcircuits each being provided with a source of voltage, means forsubjecting the screen electrode of each tube to the voltage ofthe'voltage source of the output circuit of the other tube, a resistor,and means for connecting the anode of one tube to the screen electrodeof the other tube through the resistor.

varying the magnitude of the impedance of the common portion to vary thesensitivity. 6. An electric system having, in combination,

two vacuum tubes each provided with a cathode, an anode, a controlelectrode and a screen electrode, input circuits in which the cathodesand the control electrodes of the respective tubes are respectivelyconnected, output circuits in which the cathodes and the anodes or therespective tubes are respectively connected, the

output circuits each being provided with a source oi voltage, means forsubjecting the screen electrode of each tube to the voltage of thevoltage a. An. electric system having, in combination, )5

two vacuum tubes each provided with a cathode, an anode and a controlelectrode, one 01- the tubes'having a screen electrode, input circuitsin 1 which the cathodes and the control electrodes of the respectivetubes are respectively connected,

output circuits in which the cathodes and theanodes of the respectivetubes are respectively connected, the output circuits each beingprovided with asource of voltage, means for subjecting the screenelectrode of the said one tube to the voltage of the voltage source ofthe output circuit of .the other tube, and means connecting the sourcesof voltage each between .the anode of onetube and the cathode of theother tube source of the. output circuit of the other tube, and meansfor connecting the sources or voltage each between theianode of one tubeand the cathode of the other tube with corresponding poles ofthe voltagesources connected to the 'respective cathodes.

7. An electric system having, in combination, two vacuum tubes eachprovided with a cathode, an anode, a control electrode and a screenelectrode, input circuits in which the cathodes and the controlelectrodes oi the respective tubes are respectively connected,output'circuits in which the cathodes and theanodes Io! the rewithcorresponding poles of the voltage sources connected to the respectivesaid cathodes of the said other tubes.

4. An electric system having, in combination, two vacuum tubes eachprovided with a cathode,

an anode anda control electrode, input circuits in which the cathodesand the control electrodes of the respective tubes are respectivelyconnected, output circuits in which the cathodes and the i anodes of therespective tubes are respectively spective tubes are respectivelyconnected, the

output circuits each being provided with a source of voltage, means forsubjecting the screen elec trode of each tube to the voltage of thevoltage source of the output circuit of the other tube, and means forconnecting. the sources of voltage each between the anode of one tubeand the cathode of the other tube with corresponding poles or thevoltage sources connected to the respective cathodes, the,outputcircuits having a common portion connected to the junctionconnected, the output circuits each being provided with a source ofvoltage, the output circuit of one of the tubes being coupled to theinput circuit of the other tube, and means connecting the sourcesof-voltage each between the anode of one tube and the cathode of theother tube with corresponding poles of the voltage sources connectedsubstantially directly to the respective said cathodes of the said othertubes, the output circuits having a common portion so connected betweenthe cathodes as to provide a 5 voltage drop suitable to producedegenerative coupling in the input circuit of the said other .5. Anelectric system having, in combination, two vacuum tubes each providedwith a cathode, an anode and a control electrode, input circuits inwhich the cathodes and the control electrodes of the respective tubesare respectively connected, output circuits in which the cathodes andthe anodesoi the respective tubes are respece tively connected, theoutput circuits each being" provided with a source of voltage, theoutput circuit of one of the tubes being coupled to the input circuit ofthe other tube, means connectin the sources of voltage each between theanode of one tube and the cathode oi the other tube withcorresponding'poles oi the voltage sources connected to the respectivesaid cathodes oi'the said ,other, tubes, the output circuits having acommon impedance portion so connected to the Junction .points betweenthe voltage sources and the cathodes to which the voltage sources arerespectively. connected as to provide a voltage drop suitable to producedegenerative coupling in the input circuit of the said other tube, andmeans for 1s points between the voltage sources and the cathodes towhich the tively-connected. i

8. An electric system-having, in combination, two vacuum tubes eachprovided with a cathode, an anode, a control electrode and a screenelectrode, input circuits in which the cathodes and the controlelectrodes of the respective tubesare respectively connected, outputcircuits in which the cathodes and 'the anodes of the respective voltagesources are respectubes are respectively connected, the output circuitseach being provided with a source 0! voltage, means for subjecting thescreen eleetrode or each tube to the voltage ofthe voltage source 1 ofthe output circuit of the other tube, and means for connecting thesources of voltage each between the anode of one tube and the cathode ofthe other tube with corresponding poles of the voltage sources connectedto the respective cathodes, the output circuits having a commonportionconnected to the Junction points between the voltage sources andthe cathodes to which the voltage sources are respectively: connected,and the common portion of the output circuits being provided with adegenerative resistor.

9. An electric system having, in combination,-

.an indicating instrument the control electrodes of the 'tubes arerespectively portion or the edance,

i put circuits in odes, the output circuits having a common portionconnected to the junction points between the voltage sources and thecathodes to which the voltage sources are respectively connected,

and a resistor connected in the common portion of the output circuits,and means ior effecting balance in the indicating instrument at apredetermined point of a characteristic oi. one of the tubes.-

10. An amplifier having, in combination,

anode, a control electrode and a screen electrode, input circuits in;which the cathodes and the control electrodes of the respective tubesare respectively connected, output circuits in which the cathodes andthe anodes oi the respective tubes are respectively connected, theoutput circuits each being provided with an anode battery. and means forsubjecting the screen electrode of each tube to the voltage of the anodebattery of the other tube.

.11. An amplifier having, in combination, two vacuum tubes each providedwith a cathode, an anode, a control electrode and a screen electrode,input circuits in which the cathodes and respective tubes arerespectively connected, output circuits in which the cathodes and the.anodes oi the respective connected, the output circuits each beingprovided with a source 01 volt- '-age, means for subjecting the screenelectrode of each tube to thefvoltage of the voltage source of theoutput circuit'of the other tube, the output circuits having a commonportion connected befor applying a volttween the cathodes, means age tothe input circuit of one of the tubes, the output circuit of the saidone tube having a degenerative impedance connected in the common outputcircuits and a second imand means connecting the second imthe inputcircuit 01 the said one tube.

.pedance in 12.1A voltmeter having. in combination, two ,vacuum tubeseach provided with a cathode, an

anode and a control electrode, input circuits in which the cathodes andthe control electrodes of the respective tubes are respectivelyconnected, the control electrode oi-one oi the tubes bein connected tothe anode of the other tube, out-'- which the cathodes and the anodesoithe respective tubes are respectively .connected, the output circuitseach being pro- .vided with a source of voltage, means connecting thesources of voltage each between the anode oi one tube and thecathodeof-the other tube with corresponding poles of the voltage sourcesconnected to the respective cathodes, the output circuits having acommon portion connected between the cathodes, an impedance and aninditwo vacuum tubes each provided with a cathode, an

anodes of the respective tubes are respectively connected, the outputcircuits each being provided with a source of voltage, means connectingthe sources of voltage each between the anode of one tube and thecathode of the other tube with corresponding poles or the voltagesources connected to the respective cathodes, the output circuits havinga common portion connected between the cathodes, and an impedance and anindicating instrument connected in the common portion of the outputcircuits, the impedance having a resistance substantially less than thatof the indicating instrument.

14. An alternating-current voltmeter having, in combination, two vacuumtubes each provided with a cathode, an anode, a control electrode and a.screen electrode, input circuits in which the cathodes and thecontrolelectrodes of the respective tubes are respectively connected,output circuits in which the cathodes and the anodes circuits having acommon portion connected to the junction points between the voltagesources and the cathodes to which the voltage sources are respectivelyconnected, animpedance and an indicating instrument connected in thecommon portion ofthe output circuits, one of the input circuitsincluding the connected to the said one input circuit.

15. A two-stage amplifier having, in combina- 1 .tion, two vacuum tubes,

each provided with a cathode, an anode, a control electrode and a screenelectrode, input circuits .in which the cathodes and the controlelectrodes of the respective tubes are respectively connected, outputcircuits in which the cathodes and the anodes oi the respective tubesare respectively connected, the output circuits each being provided witha source of voltage, means for subjecting the screen electrode of eachtube to the voltage of the voltage source of the output circuit of theother tube, means for applying a voltage to the input circuit of one ofthe tubes, the output circuit oi the said one tube having a degenerativeimpedance, the respective tubes with their input and output circuitsconstituting the two eating instrument connected in the common portionof the output circuits, two terminals by means of which a voltage may beapplied to the input circuit of one or the tubes, and means forconnecting one of theterminals between the impedanoe and the indicatinginstrument.

13. A voltmeter having, in combination, two vacuum tubes each providedwith a cathode, an anode and a control electrode, which the cathodes andthe control electrodes of the respective tubes are respectivelyconnected, the control electrode of one of the-tubes being connected totheanode oi the other tube, output circuits in which the cathodes andthe stages of the amplifier, and means for maintaining the potential ofthe screen electrode of one of thetubes substantially constant,independent of the output current of the amplifier, to preventdegeneration in the individual two stages of the amplifier.

16. A voltmeter having, in combination, a first vacuum tube and a secondvacuum tube each provided with a cathode, an anode and a'controlelectrode, input circuits in which the cathodes and the controlelectrodes of the respective tubes are respectively connected, outputcircuits in which the cathodes and the anodes of the respective tubesare respectively connected, the output circuits each being provided witha source of voltage, means connecting the sources 01 voltage eachbetween the anode oi one tube and the cathode of the other tube withcorresponding impedance, and a rectifier the control electrode of one orthe tubes being connected to the anode of the other tubes, outputcircuits in which the cathodes and the anodes of the respective tubesare respectively provided with a cathode, an anode and'a' controlelectrode, input circuits in which the cathodes and the controlelectrodes of the respective tubes are respectively connected, outputcircuits in which the cathodes and the anodes of the respective tubesare respectively connected, the output circuits each being provided witha source of voltage, means connecting the sources of voltage'eachbetween the anode of one tube and the cathode of the other tube withcorresponding poles of the voltage sources connected to the respectivecathodes, the control electrode of the second tube being connected tothe anode of the first tube, the output circuits having a common portionconnected to the cathodes, and an, impedance and anindicating-instrument connected in the common portion of the outputcircuits with the impedance disposed adjacent to the cathode of thefirst tube.

18. An electric system having, in combination, a first vacuum tube and asecond vacuum tube each provided with a cathode, an anode, a controlelectrode a screen electrode, input circuits in which the cathodes andthe control electrodes of the respective tubes are respectivelyconnected, output circuits in which the cathodes connected, the outputcircuits each being pro vided with a source of voltage. means connectingthe sources of. voltage each between the anode of one tube and thecathode of the other tube with corresponding poles .of the voltagesources connected to the respective cathodes, the output circuits havinga common portion connected to the junction points between the voltagesources and the cathodes to which the -voltage sources are respectivelyconnected, an

impedance and an indicating instrument connected in the common portionof the output circuits, and means for varying the impedance to vary thesensitivity of the voltmeter.

21. An electric system having, in combination, a first vacuum tube, andand a second vacuum tube each provided with a cathode, an anode, acontrol electrode, and a screen electrode, input circuits in which thecathodes and the control electrodes of the respective tubes arerespectively connected, output circuits in which the cathodes and theanodes of the respective tubes are respectively connected, the outputcircuits each being provided with a source of voltage, means forconnecting the screen electrode of one of the tubes to the voltagesource of the output circuit and the anodes oi -the .respective tubesare respectively connected, the ouput circuits each being provided witha, source of voltage, means for connecting the screbn electrode of oneof the tubes to the voltage source of the output circuit of the othertube, the outputcircuits having a common portion connected between thecathodes, animpedance and an indicating inof the other tube; the outputcircuits having a common portion connected between the oathodes,'animpedance and an indicating instrument connected in the common portionoi the output circuits, and means for varyin the output current from one01' the tubes to balance to zero the current through the indicatinginstrument.

strument connected in. the common portion of v the output circuits, avoltage-divider resistor, and means for varying the voltage-dividerresistor to adjust the zero reading of the instru ment.

' 19. An electric system having, in combination, two vacuum tubes eachprovided with a cathode, an anode and a control electrode, (inputcircuits in which the cathodes and the control electrodes of therespective tubes are respectively con-- nected, the control electrode ofone of the tubes being connected to the anode of theother tube, outputcircuits in which the cathodes and the anodes of the respective tubesarerespectively connected, the output circuits each being provided witha source of voltage, means connecting the sources otvoltage each betweenthe anode of one tube and the cathode of the other tube withcorresponding poles of the voltage sources connected tothe respectivecathodes, the output 1 circuits having a common portion connected to thejunction points between the'voltage sources and the cathodes to'whichthe voltage sources are respectively connected, an impedance connectedinthe common portion. of the output circuits, and means for varying theimpedance to vary the sensitivity of the' system. 20. A voltmeterhaving, in combination, tw

22. An amplifier having, in combination, two

vacuum tubes each provided with a cathode, an. anode and a controlelectrode, input circuits in which the cathodes and the controlelectrodes. of the respective tubes are respectively connected,

the control electrodeof one of the tubes being connected to ,the anodeof the other tube, output circuits in which the cathodes ;and the anodesof the respective tubes are respectively connected, the output circuitseach being provided with a. sourceof voltage, meansconnecting thesources of voltage each between the anode of one tube and the cathode ofthe other tube with corresponding poles of the voltage sources connectedto the respective cathodes, the

,output'circuits having a common portion connected .to the junctionpoints between the voltage sources and the cathodes to which the voltage sources are respectively connected, and i an impedance connected inthe common portion of the output circuits, the impedance having aresistance large compared to the reciprocal of the transconductance ofthe amplifier.

23. A rectifier having aninput circuit and an output circuit and having,also, a"cathode and an anode, a voltage-divider connected across; thecathode, an impedance connected in the-output circuit, and means forsimultaneously adjusting the voltage-divider and the impedance in suchratio-as to maintain the direct'potential across the impedance in theoutput circuit substantially constant in the absence or a potentialapplied to J V the rectifier. vacuum tubes each provided with a cathode,an Y 24. A voltmeter having, in combination, a first anode and a controlelectrode, input circuits in which the cathodes and the controlelectrodes of the respective tubes are respectively connected.-

' the respective tubes are .of the respective tubes are ed, outputcircuits in 8 vacuum tube and a second vacuum tube each provided with acathode, an anode and a control electrode, input circuits in which thecathodes and the control electrodes of the respective tubes arerespectively connected, output circuits in which the cathodes and theanodes of therespective' tubes are respectively connected, the outputcircuits each being provided with a source of voltage, means connectingthe sources of voltage each between the anode of one tube and thepedance and an indicating iinstrument connected in the common portion ofthe output circuits, 8

rectifier having a cathode, an anode, an input circult and an outputcircuit, means for connecting the output circuit of the rectifier to theinput circuit of the first vacuum tube, an impedance connected in theoutput circuit of the rectifier, a voltage divider connected across thecathode of the rectifier, and means for simultaneously adassure ananode, and a control electrode, one of the tubes having a screenelectrode. input circuits in which the cathodes andthe controlelectrodes of the respective tubes are respectively connected,

output circuits in which the cathodes and the anodes of. the respectivetubes are respectively connected, the output circuits each beingprovided with a source of voltage, means for subjecting justing thesecond-named impedance and the.

voltage divider to maintain the zero reading of the indicatinginstrument.

25. An electric system tube having an output circuit and provided with acathode, an anode and anauxiliary electrode, an'indicatin'g meter, meansconnectingthe indicating meter in the output circuit whereby at least aportion of the output current flows through the meter, means for sendinga current through the meter in opposition to the output current, andmeans for varying thepotential on the auxiliary electrode to balance tozero the current through the meter.

26. An amplifier having, in combination, 'a ilrst vacuum tube and asecond vacuum tube each provided with a cathode, an anode and a controlelectrode, input circuits in which the cathodes and the controlelectrodes of the respective tubes are respectively connected, outputcircuits in which the cathodes and the anodes of respectively connected,the output circuits each being, provided with a source of voltage, meansconnecting one of the sources of voltage between the cathode of thefirst tube and the anode o: the second tube, means connecting a portionof the other source of voltage between the cathode of the second tubeand the anode of the first tube, the output circuits having a commonportion connected between the cathodes and including the remainder ofthe said other source of voltage, and an impedance connected in saidcommon portion of the output circuits.

27. An electric system having, in combination,

' two vacuum tubes each provided with a cathode,

an anode, and a control electrode, one of the tubes having a screenelectrode, input circuits in which the cathodes and the controlelectrodes respectively connects which the cathodes and the anodes ofthe respective tubes are respectively connected, the output circuitseach being provided with a source of voltage, a resistor in shunt withthe voltage source of the output circuit of the other tube, and meansfor connecting the screen electrode of the said one tube to theresistor.

. 28. An electric system having, in combination, two vacuum tubes eachprovided with a cathode,

comprising a vacuum the screen electrode of the said one tube to thevoltage of the voltage source of the output circuit of the other tube,and a resistor connected between the positive terminal of the source ofvoltage of one of the tubes and the cathode oi the other tube. V

29. An electric-system having, in combination, two vacuum tubes eachprovided with a cathode, an anode and a control electrode; one of thetubes having a screen which the cathodes and the control electrodes ofthe respective tubes are respectively connected, output circuits inwhich the cathodes and the anodes (oi the respective tubes arerespectively connected, the output circuitswachbeing provided with asource of voltage, theoutput circuit of the said one tube being coupledto the'input circuit of the other the screen electrode of the said onetube to the voltage of the voltage source of the output cirthe cathodesas to provide a voltage drop suitable to produce degenerative couplingin the input circuit of the said other tube.

30. An electric system having, in combination, two vacuum tubes eachprovided with a cathode, an anode and a control electrode, inputc'rcuits in which the cathodes and the control electrodes of therespective tubes are respectively connected, means for applying avoltage to one of the input circuits, output circuits in which theoath-- odes and the anodes of the respective tubes are respectivelyconnected, the output circuits each being provided with a source ofvoltage, the output circuit of, one of the tubes being coupled to theinput circuit of the other tube, means connecting the sources of voltageeach between the anode of one tube and the cathode of the other tubewith corresponding negative poles of the voltage sources connected tothe respective said cathodes of the said other tubes, the difference inpotential between the said negative poles and the cathodes to which theyare connected being subthe voltage applied to the said one input havinga common portion connected between the cathodes, and an impedanceconnected in the common portion of the output circuits, one of the inputcircuits including the impedance, the impedancehaving a value such'as toproduce a degenerativecoupling in the said one input circuit.

31. An electric system having, in combination. two vacuum tubes eachprovided with a cathode, an anode, and a control electrode, one of thetubes having a screen electrode, input circuits in which the cathodesand the control electrodes of the respective tubes are respectivelyconnected. an impedance between said cathodes, output circults in whichthe cathodes and the anodes of the electrode, input circuits in tube,means for subjecting of direct current, means for subjecting the screenelectrode of the said one tube to the voltage of the direct-currentsource of the output circuit of the other tube, means for supplying theinput circuit of the said other tube from the output circuit of the saidone tube, and means for applying a varying voltage from an externalsource to the input circuit of the said one tube.

32. An electric system having, in combination, two vacuum tubes eachprovided with a cathode, an anode and a control electrode, an impedanceconnected between the cathodes, input circuits in which the cathodes andthe control electrodes of the respective tubes are respectivelyconnected, output circuits in which the cathodes and the and the cathodeof the other tube with corresponding poles of the voltage sourcesconnected to the respective cathodes, the output circuits having acommon portion connected between the cuit of one of the tubes, and meansfor connectanodes of the respective tubes are respectively connectingthe other end of the said one source of voltage to the anode of theother tube, and means connecting the other source of voltage between thecathode of the said other tube and the anode of the said one tube, thesources of voltage being connected with corresponding poles thereofconnected to the respective cathodes, the output circuits having acommon portion connected to the said one end of the said one source ofvoltage and the junction point between the other source of voltage andthe cathode to'which it is connected, and the remainder of the impedancebeing connected between the said one end of the said one source ofvoltage and the said junction point.

33. An electric system having, in combination, two vacuum tubes eachprovided with a cathode, an anode and a control electrode, one of thetubes having an auxiliary electrode, input circuits in which thecathodes and the control electrodes of the respective tubes arerespectively connected, output circuits in which the cathodes and theanodes of the respective tubes are respectively connected, the outputcircuits each being provided with a source of voltage, and means forconnecting the sources of voltage each between the anode of one tube andthe cathode ofthe other tube with corresponding poles of the voltagesources connected to the said respective cathodes of the said othertubes. the output circuits having a common portion connected between thevoltage sources and the cathodes, an indicating instrument and adegenerative resistor connected in the common portion of the outputcircuits, whereby a current will flow through the indicating instrument,means for varying the potential on the auxiliary electrode to balance tozero the current through the indicating instrument, and means forvarying the degenerative resistor, whereby the variation of thedegenerative resistor will not affect substantially the zero balancethrough the indicating instrument.

34. AvoItmeter having, in combination, two vacuum tubes each providedwith a cathode, an anode and a control electrode, input circuits in'which the cathodes and the control electrodes of the respective-tubesare respectively connected, the control electrode of one of the tubesbeing connected to the anode of the other tube, output circuits in whichthe cathodes and the anodes of the respective tubes are respectivelyconnected, the output circuits each being provided with a source ofvoltage, means connecting thesources of voltage each between the anodeof one tube ing one of the terminals between the impedance and theindicating instrument in order to produce degenerative coupling in thesaid input circuit.

35. A two-stage amplifier having, in combination, two vacuum tubes eachprovided with a cathode, an anode, a control electrode and a screenelectrode, input circuits in which the cathodes and the controlelectrodes of the respective tubes are respectively connected, outputcircuits in which the cathodes and the anodes of the respective tubesare respectively connected, the output circuits each being provided witha source of voltage, means for subjecting the screen electrode of eachtube to the voltage of the voltage source of the output circuit of theother tube, means for applying a voltage to the input circuit of one ofthe tubes, the output circuit of the said one tube having a degenerativeimpedance, and means connecting the sources of voltage each between theanode of one tube and the cathode of the other tube with correspondingpoles of the voltage sources connected substantially directly rto therespective said cathodes. of the said other tubes, whereby the potentialof one of the screen electrodes is maintained substantially constant,

and the respective tubes with their input and output circuitsconstituting the two stages of the amplifier.

36. An amplifier having, in combination, two vacuum tubes each providedwith a cathode, an

anode, and a control electrode, one of the tubes having a screenelectrode, input circuits in which the cathodes and the controlelectrodes of the respective tubes are respectively connected. thecontrol electrode of one of the tubes being connected to the anode ofthe other tube, output circuits in which the cathodes and the anodes ofthe respective tubes are respectively connected, the output circuitseach being provided with a source of voltage, and means for subjectingthe screen electrode of the said one tube to the voltage of the voltagesource of the output circuits of the other tube.

37. An electric system having, in combination, two vacuum tubes eachprovided with a cathode, an anode, and a control electrode, one of thetubes having a screen electrode, input circuits in which the cathodesand the control electrodes of the respective tubes are respectivelyconnected, output circuits in which the cathodes and the anodes of therespective tubes are respec cuits having a common portion connectedbetween the cathodes. 38. An electric system having, in combination,

two vacuum tubes each provided with a cathode,v

an anode; and a control electrode, one of the tubes having a screenelectrode, input circuits in which the cathodes and the controlelectrodes the output circuit oi. the other tube, the output 10 circuitshaving a common portion connected between the cathodes so as to providea voltage drop suitable to produce degenerative couplin in the inputcircuit "of the said other tube.

39. An electric system having, in combination, s

- an anode and a control electrode, input circuits in which the cathodesand the control electrodes of the respective tubes are respectivelyconnected.

two vacuum tubes each provided with a cathode, an anode and a controlelectrode, input circuits in which the cathodes and the controlelectrodes of the, respective tubes are respectively connected, outputcircuits in which the cathodes and go the anodes-of the respective tubesare respectively connected, the output circuits each being provided witha source of voltage, the output circuit of one of the tubes beingcoupled to the input circuit of the other tube, the output circultshaving a common portion connected between the, cathodes, and animpedance connected in the common portion of the output cirasoame cultsin which the cathodes and the control electrodes of the respective tubesare respectively connected, output circuits in which the cathodes andthe anodes o! the respective tubes are respectively connected, theoutput circuits each being provided with a source of voltage, the outputcircuits having a common portion connected between the cathodes, theoutpnit circuit of one of the tubes having a degenerative impedanceconnected in the common portion of the output circuits and a secondimpedance. and means connecting the second impedance in the inputcircult of the said one tube.

43. An electric system having, in combination, two vacuum tubes eachprovided with a cathode,

output circuits in which the cathodes and the anodes of the respectivetubes are respectively connected, the output circuits each beingprovided with a source of voltage, the output circuits having a commonportion connected between the cathodes, an impedance and an indicatinginstrument connected in the common portion of the output circuits, twoterminals by means of which a voltage may be applied tothe 7 inputcircuit of one oithe tubes, and means for cults, one of the inputcircuits including the impedance, the impedance having a value such asto produce a degenerative coupling in the said one input circuit.

I 40. An electric system having, in combination,

two vacuum tubes each provided with a cathode, an anode, and a controlelectrode, one otthe 5 tubes having a screen electrode, input circuitsin which the cathodes and the control electrodes of the respective tubesare respectively connected; output circuits in which the cathodes andthe anodes of the respective tubes are respectively 40 connected, theoutput circuits each being provided with a source of voltage, means forsub- Jecting the screen electrode of'the said one tube to the voltage ofthe voltage source of the output circuit oiv the other tube, and meansfor u connectingthe sources of voltage each between the anode of onetube and the cathode of the other tube with corresponding poles of thevoltage'sources connected tothe respective cathodes.

41. An electric system having, in combination,

two vacuum tubes each provided with a cathode, an anode and a controlelectrode, input circuits in which the cathodes and the controlelectrodes lot the respective tubes are respectively connected, outputcircuits in which the cathodes 55 and the anodes of the respective tubesare respectively connected, theoutput circuits each being provided witha source of voltage, and means for connecting the sources of voltageeach between the anode of onetube and the cathode of the other tube withcorresponding poles oi the voltage sources connected to the saidrespective cathodes of the :said other tubes, the output circuits havinga common portion connected'between the voltage sources and the as meansfor balancing to zero the current through the indicating instrument, andmeans for varying the degenerative resistor.

42. An electric system having, in combination, two vacuum tubes eachprovided with a cathode,

arilanode, and a control electrode, input cir- 7 being provided with asource of connecting one of the terminals between the im-, pedance andthe indicating instrument in order to produce degenerative coupling inthe said input circuit.

.44. An electricsystem having, in combination,

two'vacuum tubes each provided with a cam ode, an'anode, and a controlelectr one of the tubes having a cults in trodes of the respective tubesare respectively connected, output circuits in which the cathodes tubesare reand the anodes of the'respective spectively connected, the outputcircuits each voltage, means for subjecting the screen'electrode of thesaid one tube to the voltage of the voltage source of the-outputcircuit'of the other tube, the output. circuits having a common portionconnected between the cathodes, and an impedance and an indicatinginstrument connected hr the common portion of the output circuits.

45. An electric system having, two vacuum tubes each provided with acathode, an anodeand a control electrode, input circuits in which thecathodes and the control elec-.=

trodes of the respective tubes ar respectively connected, outputcircuits in which the cathodes and' the anodes or the respective tubesare respectively connected, the output circuits each being providedwitha source of voltage, the output circuits between the cathodes, animpedance and an in-, dicating instrument connected in the commonportion oi the output circuits, and means for varying the output currentfrom one of the tubes to balance to zero the current through theindicating instrument.

46'. An electric system having, in combination, two vacuum tubes eachprovided with a cathode, an anode and a control electrode, inputcircuits in which the cathodes and the control electrodes of therespective tubes are respectively connected. output circuits in whichthe cathodes and the anodes oi the respective tubes are respectivelyconnected, the output circuits each being provided with a source oivoltage, the output circuits having a common portion'connected betweenthe screen electrodefinput cir- V which the cathodes and thecontrclelecin combination,

having a common portion connected" ,means for varying thevoltage-divider resistor to adjust the zero reading of the instrument.

4?. An electric system having, in combination,

vacuum-tube apparatus having an impedance and an indicating instrument,a rectifier having a cathode, an anode, an input circuit and an outputcircuit, means for connecting the output circuit to the vacuum-tubeapparatus, an impedance connected in the output circuit, a voltagedivider connected across the cathode. and means for simultaneouslyadjusting the voltage divider and the impedance to maintain the zeroreading of the indicating instrument. u

WILLIAM NORRIS TUTTLE.

